1. Field of the Invention
The present invention relates to a vibrating plate according to the preamble of patent claim 1. Vibrating plates for soil compaction standardly have a lower mass that includes, inter alia, a soil contact plate that compacts the soil and a vibration exciter device that charges the soil contact plate, as well as an upper mass that is connected to the lower mass via a spring device; the drive, for example, being considered as part of the upper mass.
2. Description of the Related Art
Reversible vibration plates, i.e. vibration plates whose direction of travel can be switched at least between the forward and backward direction, are standardly realized in what is known as two-shaft technology. Such machines are either operable via remote control or are manually guided. In manually guided vibration plates, attached to the upper mass there is a guide drawbar on whose head there are provided elements for controlling the direction of travel. Using these travel direction control elements, inter alia the vibration exciter can be controlled so as to produce a vibration having a resultant force whose horizontal direction of action is oriented in the direction desired by the operator. Moreover, the travel direction control elements usually have a robust construction, so that the operator can also influence the direction of travel of the vibration plate through the manual introduction of force, or can even steer the vibration plate.
In vibrating plates that use two-shaft technology, the vibration exciter situated on the lower mass has two imbalance shafts that are capable of rotation in opposite directions. The imbalance shafts are coupled to one another with a positive fit so as to be capable of rotation, so that the front shaft rotates backward and the rear shaft rotates forward. The imbalance masses borne by the two shafts are rotated by 90° relative to one another in the initial position.
A vibrating plate of this type is known e.g. from WO 02/35005 A1.
FIG. 1 schematically shows a side view of a vibrating plate known from the prior art. On a soil contact plate 1, there is situated a vibration exciter formed from a front imbalance shaft 2 and a rear imbalance shaft 3. Via a spring device 4 made up of a plurality of springs, an upper mass 5 is connected to soil contact plate 1. In upper mass 5, there is provided a drive (not shown) for the vibration exciter. In addition, a drawbar 6 having an operating element 7 is attached to upper mass 5.
In the vibration exciter, on imbalance shafts 2, 3 there are attached imbalance masses 8 and 9 respectively, which in the initial position shown in FIG. 1 are rotated by 90° to one another. The opposite rotation of imbalance shafts 2, 3 gives rise to a resultant force vector 10 that at all times is inclined by 45° to the surface of the soil, i.e. the plane defined by soil contact plate 1. The impact of the lower mass, formed essentially by soil contact plate 1 and the vibration exciter, results in soil compaction. Of the nominally existing overall imbalance force, due to the angular setting about 70% is used for compaction (vertical force component) and for propulsion (horizontal force component) respectively.
One of the two imbalance masses 8, 9 can be rotated by up to 180° on the associated imbalance shaft 2, 3. Alternatively, it is also possible to modify the overall phase position between the two imbalance shafts 2, 3. This creates the possibility of forward and backward controlling, as well as vibration in place, in which there is then 100% compaction with no horizontal movement.
FIG. 2 shows, in analogy to FIG. 1, a schematic representation of the vibrating plate, the phase position of imbalance shaft 3 with imbalance mass 9 being modified by 180° relative to the position shown in FIG. 1. This gives rise to a resultant force vector 10 that is essentially directed toward the rear with an angle of 45° to soil contact plate 1, thus bringing about backward travel of the vibrating plate. The corresponding modification of the phase position in the vibration exciter was brought about in a known manner by actuating operating element 7, i.e., pulling back on operating element 7.
In order to modify the phase position between imbalance masses 8, 9, or imbalance shafts 2, 3, a turning sleeve is standardly used that is fashioned such that e.g. the imbalance mass that is to be adjusted is guided in the direction of the shaft along a spiral groove, thus moving through the corresponding angle of rotation. Instead of a turning sleeve, other adjustment elements are known, such as differential or planetary drive. This technology has long been known, so that a more detailed description is not necessary here.
For particular cases of application (e.g. travel on poorly compactable material such as sand, during asphalt work, or during paving vibration), the compaction effect is less important than is a rapid propulsion of the vibrating plate. In practice, in such cases one sometimes makes do by modifying the angle between imbalance masses 8, 9 on shafts 2, 3 in such a way that the resultant force vector 10 runs more flatly. In FIG. 3, as an example a relative position of imbalance masses 8, 9 is shown in which a resultant force vector 10 results whose angle of force action is less than 45°. Correspondingly, force vector 10 has a larger horizontal component, which achieves a stronger propulsion. Conversely, the vertical component of force vector 10 is reduced, so that the compaction effect is correspondingly less.
The flatter position of force vector 10 shown in FIG. 3 can take place e.g. by “re-hanging” imbalance shafts 2, 3 by one or more teeth on the 1:1 gear mechanism between imbalance shafts 2, 3. Another possibility is to use a turning sleeve that has a steeper inclination, causing an angular rotation of more than 180°.
If imbalance shafts 2, 3 are “re-hung” by one or more teeth, an enlargement of the horizontal component of the force vector can be achieved in only one direction, preferably the forward direction. In contrast, in the other direction the horizontal component is reduced, as can be seen in FIG. 4, in which imbalance shafts 2, 3, beginning from the position according to FIG. 3, are pivoted into rearward travel. Due to the large vertical portion of force vector 10 during rearward travel, the vibrating plate runs very roughly, making it impossible to use it on asphalt or for paving work.
In this case, a turning sleeve having a steep inclination of the guide groove is advantageous, which also enables a faster propulsion during rearward travel, corresponding to the propulsion in the forward direction, as is shown schematically in FIG. 5.
A disadvantage of both variants is that simultaneously with the vertical compaction force component, the force component that lifts soil contact plate 1 from the soil between the individual compacting strokes is also reduced. This is because the soil contact plate can spring from the soil being compacted and move forward in the desired manner only if there is a sufficiently large vertical force component. On flat ground, this is uncritical within large ranges of the angular position of force vector 10. However, when gradients in the soil have to be traveled over, the vertical force is often no longer sufficient to lift the lower mass up from the soil far enough to climb the gradient as a result of the forward-oriented horizontal force.
FIG. 6 shows such a case of application, in which a vibrating plate having a force vector 10 set flat (force action angle less than 45°) is climbing up a gradient. In this situation, there is a high probability that the vibrating plate will remain stationary even though the force component in the direction of movement (horizontal component relative to soil contact plate 1) was increased. This effect is often not comprehensible to the operator of the vibrating plate, and also hinders effective work.